1. Field of the Invention
This invention relates to an integrated radiation image recording and read-out apparatus comprising an image recording section for exposing a stimulable phosphor sheet to a radiation passing through an object to have a radiation image of the object stored thereon, an image read-out section for exposing the stimulable phosphor sheet to stimulating rays which cause them to emit light in proportion to the stored radiation energy, and detecting and converting the emitted light into electric signals which are used to reproduce a visible image from the read-out image information, and an erasing section for releasing the radiation energy remaining on said stimulable phosphor sheet after read-out. This invention particularly relates to such an apparatus in which stimulable phosphor sheets are circulated and reused for recording images and more particularly to such an apparatus in which mammography is conducted in the image recording section.
2. Description of the Prior Art
When certain kinds of phosphors are exposed to a radiation such as X-rays, .alpha.-rays, .beta.-rays, .gamma.-rays, cathode rays or ultraviolet rays, they store a part of the energy of the radiation. Then, when the phosphor which has been exposed to the radiation is exposed to stimulating rays such as visible light, light is emitted from the phosphor in proportion to the stored energy of the radiation. A phosphor exhibiting such properties is referred to as a stimulable phosphor.
As disclosed for example in Japanese unexamined patent publication No. 56(1981)-11395 and U.S. Pat. Nos. 4,258,264, 4,315,318, 4,387,428 and 4,276,473, it has been proposed to use a stimulable phosphor in a radiation image recording and reproducing system. Specifically, a sheet comprising the stimulable phosphor (hereinafter referred to as a stimulable phosphor sheet) is first exposed to a radiation passing through an object such as a part of the human body to have a radiation image stored thereon, and then is scanned with stimulating rays which cause it to emit light in proportion to the radiation energy stored. The light emitted from the stimulable phosphor sheet when the sheet is exposed to the stimulating rays is photoelectrically detected and converted to an electric image signal, which is processed so as to reproduce a visible image having an improved quality, particularly a high diagnostic efficiency and accuracy. The finally obtained visible image may be reproduced in the form of a hard copy or may be displayed on a cathode ray tube (CRT). In this radiation image recording and reproducing system, the stimulable phosphor sheet is used only for temporarily storing the radiation image in order to reproduce the final visible image therefrom in a final recording medium. For economical reasons, therefore, it is desirable that the stimulable phosphor sheet be used repeatedly.
Further, in a mobile X-ray diagnostic station such as a traveling X-ray diagnostic station in the form of a vehicle like a bus which is provided with a radiation image recording and read-out apparatus for use in the aforesaid radiation image radiation recording and reproducing system and moves from place to place to record radiation images for mass medical examinations, it is disadvantageous to load the mobile X-ray diagnostic station with a large number of stimulable phosphor sheets, and the number of stimulable phosphor sheets loaded on the mobile X-ray diagnostic station should be minimized. Therefore, it is desirable to load the mobile X-ray diagnostic station with stimulable phosphor sheets which can be used repeatedly, once store the radiation images of the objects on the stimulable phosphor sheets, transfer the electric image signals read out from the stimulable phosphor sheets onto a recording medium having a large storage capacity, such as a magnetic tape, and circulate and reuse the stimulable phosphor sheets for further image recording and read-out operations, thereby to obtain the radiation image signals of many objects. Further, when image recording is conducted continuously by circulating and reusing the stimulable phosphor sheets, it becomes possible to increase the image recording speed in mass medical examinations. This is very advantageous in practical use.
In order to reuse stimulable phosphor sheets as described above, the radiation energy remaining on the stimulable phosphor sheet after it is scanned with stimulating rays to read out the radiation image stored thereon should be eliminated or erased as described, for example, in Japanese unexamined patent publication No. 56(1981)-12599 and U.S. Pat. No. 4,470,619. The stimulable phosphor sheet can then be used again for radiation image recording.
From the practical point of view, therefore, it is very convenient to use an integrated apparatus in which at least one stimulable phosphor sheet is reused by repeatedly circulating it through an image recording section for recording a radiation transmission image of an object on the stimulable phosphor sheet by exposing it to a radiation passing through the object, an image read-out section for reading-out the radiation image stored on the stimulable phosphor sheet in the image recording section, and an erasing section for releasing the radiation energy remaining on the stimulable phosphor sheet after read-out so as to prepare it for recording of the next image thereon. This is because such an integrated apparatus can be easily installed in a mobile X-ray diagnostic station, thus making it easier to move from place to place for mass examinations, or in a hospital or the like.
The applicant therefore proposed in U.S. patent application No. 600,689 an integrated radiation image recording and read-out apparatus comprising an image recording section, an image read-out section and an erasing section built into a single unit further provided with a circulation and conveyance system for enabling circulation and reuse of at least one stimulable phosphor sheet.
On the other hand, various different types of radiation image recording apparatuses are used depending on the part of the human body to be examined and in some of these apparatuses it is difficult to integrate the image recording apparatus with an image read-out section and an erasing section. This is true, for example, in the case of the mammographic radiation image recording apparatus used for carrying out examinations for detecting breast cancer.
In a mammographic radiation image recording apparatus it is necessary to be able to record radiation images at different angles with respect to the breast. The apparatus therefore has to be constructed so as to allow the radiation source and the image recording medium to revolve unitarily about the breast being mammographed. Thus, when an attempt is made to use a stimulable phosphor sheet as the image recording medium in the mammographic radiation image recording apparatus and to construct the apparatus so that the mammographic radiation image recording apparatus is integrated with an image read-out section and an erasing section, the structure becomes mechanically complex because of the need to revolve the heavy image read-out section and/or erasing section together with the image recording section and, moreover, the amount of power required for revolving these sections becomes disadvantageously large.